In a related art, in order to improve electrical properties of a thin film transistor device on a display substrate, a thin film transistor of dual-gate structure (i.e., an upper gate and a bottom gate) may be fabricated. However, two gate electrodes and a source electrode and a drain electrode of the thin film transistor of dual-gate structure are usually formed by using different masks, the thin film transistor of dual-gate structure fabricated in this way has a large parasitic capacitance. With constant improvement in display size and resolution, a sum of all parasitic capacitances of the thin film transistors on an array substrate will become relatively large, which may directly degrade performance of a display device.